Diorganopolysiloxanes carrying a single aliphatically unsaturated organic group at one molecular chain terminal and silanol at the other terminal are known in the art. Diorganopolysiloxanes of this type can be synthesized, for example, by the anionic polymerization of cyclic siloxane using a lithium catalyst and methacryloxypropyldimethylsilanol as initiator, as disclosed in Japanese Patent Publication Kokai Number Hei 1-98631. Alternatively, diorganopolysiloxanes of this type can be synthesized by the polymerization of cyclic trisiloxane on the alkali metal salt of methacryloxypropyldimethylsilanol with termination of the polymerization by acetic acid, as disclosed in Japanese Patent Publication Kokai Number Hei 2-92933. However, neither of these methods can synthesize a macromonomer carrying 2 or 3 aliphatically unsaturated organic groups at one molecular chain terminal and silanol or various other functional groups at the other molecular chain terminal.
In addition, macromonomers carrying 2 or 3 aliphatically unsaturated organic groups at the molecular chain terminals and in which siloxane units are bonded across a divalent hydrocarbon group are known as a starting substance for ultraviolet curing as disclosed in Japanese Patent Publication Number Sho 63-183930. The organopolysiloxane-type polymer disclosed is synthesized by the platinum-catalyzed addition reaction of methyldichlorosilane to .alpha.,.omega.-divinyldimethylsiloxane followed by reaction of the product with acryloxymethyldimethylsilanol in the presence of an HCl scavenger. Thus, this synthesis method can provide only organopolysiloxane-type polymers having the same number of aliphatically unsaturated organic groups at both molecular chain terminals, and this method is also incapable of introducing different organic groups in a controllable manner at the two terminals.
Japanese Patent Publication Kokai Number Hei 10-158406 discloses an organopolysiloxane-type polymer that carries 1 aliphatically unsaturated organic group at one molecular chain terminal and 2 or 3 diorganohydrogensiloxy groups at the other chain terminal. Highly branched polysiloxanes (hyperbranched polymers) can be synthesized, for example, by the platinum-catalyzed addition reaction of this organopolysiloxane-type polymer. However, when the highly branched polysiloxane product is held in long-term storage, the silicon-bonded hydrogen atoms in the polymer gradually undergo hydrolysis and condensation due to the platinum catalyst. The result is an increase in the molecular weight, which makes it impossible to produce this polymer in a constant molecular weight form.
Therefore, it is an object of this invention to provide a novel macromonomer that carries 2 or 3 aliphatically unsaturated organic groups at one molecular chain terminal, carries silanol or various other functional groups at the other terminal, and contains siloxane units bonded across a divalent hydrocarbon group. Another object of the present invention is to provide methods for the synthesis of this novel macromonomer.
It is a further object of this invention to provide a hyperbranched polymer made from a macromonomer. Hyperbranched refers to a class of very highly branched polymers which tend to be globular in form. Various types of hyperbranched polymers, which are represented by the Starburst.TM. dendrimers (treelike polymers), are known. These hyperbranched polymers have higher functional group densities per molecular unit than straight-chain polymers and conventional branched polymers. Another characteristic feature of the hyperbranched polymers is that they possess an internal space once they have been elaborated to several generations. These characteristics point to potential applications as surfactants, gelling agents, drug delivery systems, polymeric absorbents, and the like.
Additionally, introduction of the siloxane bond into the hyperbranched polymer format could provide a hyperbranched polymer that possesses the unique features of polysiloxanes. Various polysiloxane-based hyperbranched polymers have already been proposed. Hyperbranched siloxane polymers can have a SiH surface or an alkenyl or alkynyl surface. However, it is difficult to prepare hyperbranched polymers with a SiH surface because of several factors, including the instability of the SiH precursors, difficulty in controlling the reaction to prevent crosslinking, and difficulty in preventing side reactions during storage. For example, JP-A 03-263,431 teaches a method for synthesizing a SiH-functional polysiloxane dendrimer by repeating a multi-step reaction that includes condensation of the SiCl and SiOH groups and hydrolysis of the SiH group. This method, however, is unsuitable for large-scale industrial production due to its complex synthetic procedure and low overall yield.
In Organometallic News, 40-42 (1993), a method is proposed for the synthesis of a SiH-functional polysiloxane dendrimer by reacting polyfunctional chlorosilane with 1,1,3,3-tetramethyldisiloxane in the presence of hydrochloric acid to replace the chlorine atom of SiCl with the dimethylsiloxy group. Since these synthetic methods are each multi-step reactions with isolation and purification at each step, they offer the advantage of producing dendrimers with defined structures and narrow molecular weight distributions. However, they require repetition of the reaction process a number of times in order to obtain dendrimer of the desired generation and they have low overall yields, and these features make them very unsuitable for large-scale industrial production.
Hyperbranched poly(siloxysilanes)are described by Mathias and Carothers in J. Am. Chem. Soc. 1991, 113, 4043-4044. A monomer of the formula Vi(CH.sub.2)Si(OSiMe.sub.2 H).sub.3, where Vi is vinyl and Me is methyl, is polymerized using a platinum hydrosilylation catalyst. The resulting hyperbranched polymer with a SiH surface can be stabilized by capping with allylphenylether.
In contrast, in J. Inorg. Organomet. Polym. 4(1), 61-77 (1994) a single-step method is proposed for obtaining SiH-functional or Si-vinyl-functional hyperbranched polysiloxane by the intermolecular hydrosilylation reaction of vinyltris(dimethylsiloxy)silane or tris(vinyldimethylsiloxy)silane. While this method cannot provide a narrow molecular weight distribution or defined-structure dendrimer, it nevertheless offers the advantage of providing a Si-functionalized hyperbranched polysiloxane in a single step and has the potential for large-scale industrial production.
Due to the close proximity of the silicon-bonded hydrogen and vinyl in this method, steric hindrance increases in association with the development of the hydrosilylation reaction to such a degree that bringing the reaction to completion becomes quite problematic. In addition, this method has been unable to bring the properties characteristic of polysiloxanes to the hyperbranched polymer format because it gives polymer that has the silethylenesiloxane structure.
As a consequence, a highly reactive, SiH-functional polysiloxane that can provide SiH-functional hyperbranched polysiloxane in a single step is desired. Specifically, a further object of this invention is to provide an organopolysiloxane macromonomer and a method for its preparation. The macromonomer carries an aliphatically unsaturated organic group at one molecular chain terminal and silicon bonded hydrogen atoms at the other terminal. A further object of the invention is to provide a hyperbranched polymer by polymerizing the macromonomer. A further object of this invention is to provide a method for stabilizing the hyperbranched polymer.